1. Field of the Invention
This invention relates to optical packet transmission. The invention is based on a priority application EP 01440076.6, which is hereby incorporated by reference.
2. Background of the Invention
The increased demand for high speed communication networks transmitting voice and/or data at high data rates provided several alternatives of networks; electric networks like SDH or ATM, electro-optical networks, e.g. SONET, optical transmission of SDH, ATM, and all-optical networks, the latter not being implemented yet. The network topologies could be ring, star, mesh, bus, etc. In the optical domain both voice and data are generally transmitted via optical fibers using wavelength division multiplex (WDM) or dense WDM (DWDM). At nodes within the network add drop multiplexers are used to drop received information and to add new information to be transmitted over the network. Cross-connects are used to switch information. It is a wish not to perform optical to electrical conversion and electrical to optical conversion for the information to be forwarded in an add drop multiplexer. At the same time adding and dropping of information should be as simple as possible and interferences should be minimized.
Some examples of implementations can be found in the following patent applications.
In EP 1 009 120 A2 a band optical add drop multiplexer for a wavelength multiplexed communication network is discloses, which comprises a wide-band demultiplexer for receiving an input multichannel optical signal and separating same into a first multichannel optical signal of a first band, e.g. for dropping purpose, and a second multichannel optical signal of a second band, e.g. for forwarding purpose; and a wide-band multiplexer for combining a third multichannel signal of a third band, e.g. for adding purpose, with said second multichannel optical signal to obtain an output multichannel optical signal.
In EP 1 065 820 A2 an add drop arrangement capable of adding and dropping at least one optical channel of a wavelength division multiplexed (WDM) signal in a WDM ring network having a plurality of nodes connected over an optical fiber facility is disclosed. The arrangement comprises in at least one of the plurality of nodes a broadband optical coupler including a first input coupled to the optical fiber facility for receiving the WDM signal, a first output for passing a topped first portion of optical signal power of the WDM signal, and a second output for passing a second portion of optical signal power of the WDM signal to the WDM ring network, a receiver coupled to the first output, the receiver capable of extracting at least one optical channel from the tapped first portion, and a transmitter coupled to a second input of the broadband optical coupler, the transmitter capable of supplying an optical channel to be added to the WDM signal; and in at least one of the plurality of nodes, a means for preventing re-circulation of an optical channel to substantially reduce interference between optical channels transported in the WDM ring network.
In WO 00/49752 an add drop multilexer is discloses which has a group filter that divides an incoming WDM signal into several channel groups of corresponding adjacent WDM channels. A reconfiguration module is ferd to each channel group. A first type of module makes it possible to perform manual configuration of the add drop channels and the coupled WDM channels while a second type of module makes it possible to carry out remote configuration. A fourth type of module enables remote configuration of the drop continue channels.
Each of the above examples of implementations has his advantages and disadvantages. A alternative solution is looked for.